I've never been in the New England Patriots' locker room, but I've read in the Boston Globe that there is a huge sign in there with the words "DO YOUR JOB" in all capital letters.  The implication is that if every individual player does his job and does it well, then the team as a whole will win.

Every person on the Patriots has a unique role to play in the game.  The team only succeeds if each individual focuses on doing his job as best he can.  Because the Patriots are so good at doing their own jobs, they've won three Super Bowls and were named USA Today's Franchise of the Decade. 
I'd submit that the same rule applies in the world of business.  Marketing needs to identify opportunities and unique value propositions.  Sales needs to build customer relationships and sell. Product managers need to design great products with the features that matter to customers.  Engineering needs to write great code.  If everyone does their job, then the company succeeds.

Where it starts to fall apart is if people start doing each other's job.  Perhaps product management feels that marketing is capturing the right value in the product, so product managers start building shadow presentations that they give to sales.  Or perhaps sales feels that PM is putting the right features in the product, so they start going to engineering with specific product features that they need put into the process.  Pretty soon, you have complete chaos and a dysfunctional organization. 

What people forget when they try to do other people's jobs is that many times what looks easy on the surface isn't actually all that easy when you are the one who has to deliver.  In many cases, people have advanced degrees (MBA or MS in Computer Science) that qualify them for their job, or they have years of experience. 

As a marketing professional, I'd submit that the marketing function feels this pain more acutely than other functions.  I'm never going to sit down and have an engineering schedule review.  Nor am I going to assess the QA methodology of an engineering organization.  But as human beings, we are all exposed to marketing 200 times a day in our personal lives — through TV, internet, even our friends trying to get us to join their gym.  And we know what we like and what we don't like, and what messages resonate with us. 

Marketing is both an art and a science, and the art part of it is almost entirely subjective.  So an engineer may not be qualified to evaluate a lead process flow, but she will certainly know if an advertisement speaks to her or not, or if she thinks the messaging accurately conveys the product that she has built.  But what's missing here is that this engineer's opinion belongs to an audience of one, and you never want to market to an audience of one.  As a marketer, you need to be able to craft a value proposition that speaks simultaneously to customers, partners, employees, investors, analysts, press, and prospects.

It's oftentimes easier to criticize than to create.  And tone most definitely matters.  When our friendly engineer offers her suggestions for improvement, if it's offered in the spirit of constructive criticism, then more often or not, the marketing team will consider it.  However, what is often missing is that we may have tested this idea with several customer focus groups and gotten their feedback.  Or we may have spoken with industry analysts who told us to position the product in a specific way to speak to an unmet need they are hearing from their customers. 

Now, it's our job as marketers to communicate that information back to our constituents inside the organization.  After all, we have the privilege of being the external voice to the market, representing our company and the work of all the employees.  We need to be both external AND internal marketers, to explain why the path we took is the right one.  But it's a fine line.  We don't want to spend so much time marketing internally that we forget to market externally.

As marketers, we need to become ever more adept at listening to all the feedback from all constituencies inside and outside our organization.  But we need to keep in mind that there will be ever more feedback than we can possible incorporate into the message.  And if we do incorporate it all, then the message becomes watered down, and speaks to no one.  A good marketer will consider all the feedback, keep the valuable pieces and then have the courage to discard the other pieces.  And then have the courage to stand by that decision, even in the face of fire. 

Net-net, this is not an easy problem to solve... and nor should it be.  I'll be honest... it's tempting sometimes to do someone else's job... I have ideas for product feature sets, and I've been in meetings with sales guys where I think to myself, "I could do a better pitch than this!"  But the only way for a company to succeed and thrive is if we have granted trust that individuals doing a job actually know what they are doing.

After all, everyone wants to be Tom Brady.  But if Tom Brady didn't have Matt Light to protect him, then Tom would spend most of the game on his back and wouldn't be able to complete all those passes to Randy Moss.  And the Patriots wouldn't be three-time Super Bowl champions.